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Ch.19 Enzymes and Vitamins
Chapter 19, Problem 30

What type of enzyme regulation occurs in the following situations?


a. Buildup of the product of the pathway that converts glucose to pyruvate stops at the first enzyme in the multistep process.

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1
Identify the type of enzyme regulation described in the problem. This involves understanding how the buildup of a product affects the enzyme activity.
Recognize that the situation describes a feedback mechanism where the end product of a pathway inhibits an enzyme that acts earlier in the pathway.
Understand that this type of regulation is known as feedback inhibition, a common method of metabolic control.
Feedback inhibition typically involves the end product binding to an allosteric site on the enzyme, causing a conformational change that reduces its activity.
Conclude that the regulation described is a form of negative feedback, where the accumulation of the product inhibits the pathway to prevent overproduction.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Feedback Inhibition

Feedback inhibition is a regulatory mechanism in metabolic pathways where the accumulation of an end product inhibits an earlier step in the pathway. This prevents the overproduction of the product and helps maintain homeostasis within the cell. In the context of the question, the buildup of pyruvate would signal the first enzyme to slow down or stop its activity, thereby regulating the flow of glucose conversion.
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Feedback Control Example 1

Enzyme Kinetics

Enzyme kinetics refers to the study of the rates of enzyme-catalyzed reactions and how they change in response to various factors, including substrate concentration and the presence of inhibitors. Understanding enzyme kinetics is crucial for analyzing how enzymes respond to changes in product levels, as it provides insight into how feedback mechanisms can alter reaction rates and overall metabolic flow.
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Allosteric Regulation

Allosteric regulation involves the binding of regulatory molecules to an enzyme at sites other than the active site, leading to conformational changes that affect enzyme activity. This type of regulation can enhance or inhibit enzyme function, allowing for fine-tuned control of metabolic pathways. In the scenario presented, the accumulation of the product may act as an allosteric inhibitor, affecting the first enzyme's activity in the glucose to pyruvate conversion pathway.
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Related Practice
Textbook Question

Apple slices and peeled potatoes rapidly brown in open air due to the presence of phenolases. Phenolases cause the oxidation of phenolic molecules like tyrosine to quinones, colored molecules responsible for the brown colors seen. An experiment comparing the time it took for a change to occur in the color of apple slices versus potato slices was done to test for phenolase activity. Then, a second experiment was done with new apple and potato slices with H2O2 measuring time until bubbles appeared. <IMAGE>


b. Which sample contains more catalase? Why?

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Textbook Question

The reaction that follows is catalyzed by isocitrate dehydrogenase and occurs in two steps, the first of which (step A) is formation of an unstable intermediates (shown in brackets).


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d. To what class of enzymes does isocitrate dehydrogenase, the enzyme that catalyzes this reaction, belong?

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Textbook Question

Serotonin is a monoamine neurotransmitter. It is formed in the body from the amino acid tryptophan (Figure 28.6, p. 836). What class of enzyme catalyzes each of the two steps that convert tryptophan to serotonin?

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Textbook Question

How do you explain the observation that pepsin, a digestive enzyme found in the stomach, has a high catalytic activity at pH 1.5, while trypsin, an enzyme of the small intestine, has no activity at pH 1.5?

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Textbook Question

What are the cellular advantages to feedback inhibition?

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Textbook Question

Activation of a zymogen is by covalent modification. How might phosphorylation or dephosphorylation (also covalent modification) modify an enzyme to make it more active (or more inactive)?

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